When dealing with mechanical designing, there is a need to reduce frictions by lubricating rotating members by means of an oil bath. In many applications, portions of the rotating members must be immersed in an oil bath and other portions adjacent thereto must work in a sealed environment in the absence of oil. In order to fulfil this need, seal assemblies are known, for example, from patent EP-B-2058563, said seal assemblies being designed to be housed in the compartment defined between a hollow casing, which is usually fixed, and a rotating organ housed on the inside. These assemblies, during the rotation of the rotating member, make sure that the aforesaid compartment is sealed, so as to prevent oil from flowing towards the environment that needs to operate in dry conditions.
In particular, these seal assemblies have an axial symmetry with respect to the axis of the rotating member to which they are coupled and substantially consist of a radially inner ring, which is made of a metal material and is fixed to the rotating member, of a radially outer ring, which is also made of a metal material and is fixed to the casing, and of a seal element, which is made of an elastically deformable polymer material and is interposed between the aforesaid rings.
More precisely, the elastomer material is carried by the outer ring and has, on the side facing the oil bath, a first seal lip, which is adapted to create a contact seal with a relative first coupling portion of the inner ring.
In order to reduce the typical drawback of contact seals, namely the quick operating wear of the elastomer material in the area of cooperation with the metal ring, the first seal lip is provided with a spiral groove, which has a double effect:                it allows the seal action to be implemented by means of a simple surface contact between the first elastomer material seal lip and the inner ring, namely without any penetration of the first one into the second one; and        thanks to the rotation of the inner ring, which is integral to the rotating member, it permits the generation of a fluid-dynamic “pumping” action for the air contained between the first seal lip and the inner ring, so as to push the oil towards the environment intended for it, thus increasing the sealing effect.        
Furthermore, known seal assemblies comprise a second seal lip, which is adapted to cooperate with a second coupling portion of the inner ring, which is axially interposed between the first coupling portion and the dry environment. The second seal lip is available in a configuration of sealing contact with the second coupling portion, in case the rotating member is still, and in a configuration of detachment from the second coupling portion, in case of rotation of the rotating member. The second seal lip permits a stabilization of the respective seal assembly in static conditions compared to the seal assemblies that do not have said second lip.
The seal assemblies described above, despite ensuring a good operation in dynamic conditions, are affected by some drawbacks in static conditions.
In particular, seal assemblies of the type described above are not capable of ensuring a perfect seal of the dry environment when the rotating member is still and is arranged so as to be inclined with respect to the horizontal line, or in all those cases in which the oil level—with a still rotating member—exceeds half the rotating member itself.
In this situation, indeed, part of the seal assembly can find itself in an oil bath and the first seal lip, which is provided with the spiral groove, is not capable of ensuring, in static conditions, the same sealing action generated in dynamic conditions, namely with the help of the fluid-dynamic pumping action used to pump the oil towards the environment intended for it.
The aforesaid situation can occur, for example, when the vehicle on which the rotating member is fitted is standing still on a slope or in case the aforesaid rotating organ is mounted in an oblique position in the vehicle itself.
Furthermore, some assemblies can experience an overturning of the first seal lip in conditions of positive pressure originating from the oil bath environment, resulting in the complete loss of functionality of the seal assembly.
Moreover, in vacuum conditions on the side of the oil bath environment there can be undesired vibrations and noises.